Audio cassettes of the dual spool type generally called "Phillips" Cassettes commonly include shims between side surfaces of the spools and a case of the cassette. The purpose of the shims is to reduce friction against the sides of the spools and coils of tape wound around the spools as they rotate during use of the cassette, and to guide the tape as it is wound onto and off of the spools. Typically the shims have a plurality of raised portions formed by creasing or embossing that are found on various portions of the shim and may extend in various directions such as longitudinally of the shim or radially of the spools, which raised portions are intended to help these functions, and various patents such as U.S. Pat. No. 3,891,159 describe various patterns for these creases.
Such raised portions in a shim, however, do not always provide the degree of resilience for the shim that is desirable to center the spools and coils of tape, and the raised portions of the shims can provide areas of high wear concentration and can catch on portions of the spools or wound tape as the spools are rotated to move the tape therebetween, thus causing irregular movement of the tape and resultant distortions of the signals being read from the tape.